It has been known that irradiation of short pulse laser to the inside of a transparent medium causes chemical and physical changes in the inner structure of the medium as a result of the nonlinear optical effect. It is therefore possible to record the information inside the transparent medium by means of the structural change. Patent Literature 1 discusses the three-dimensional memory for information recording by utilizing the structural change of the recording medium as the recording bit. When recording the information by using the short pulse laser, the laser beam is divided into a plurality of spots for increasing the recording speed so that information data of multiple bits is simultaneously recorded. Specifically, Nonpatent Literature 1 discloses the technique which allows the spatial optical modulator to divide the laser beam into a plurality of spots for irradiating the quartz glass so as to ensure batch recording of information data of the multiple bits inside the quartz glass.